Shell Mass Properties
dynamics node

The Shell Mass Properties DOP defines the surface mass density for the polygons of a Cloth Object.

Parameters

Inputs

First Input

This optional input can be used to control which simulation objects
are modified by this node. Any objects connected through this input
and which match the Group parameter field will be modified.

If this input is not connected, this node can be used in conjunction with an
Apply Data node, or can be used as an input to another data node.

All Other Inputs

If this node has more input connectors, other data nodes can be
attached to act as modifiers for the data created by this node.

The specific types of subdata that are meaningful vary from node to
node. Click an input connector to see a list of available
data nodes that can be meaningfully attached.

Outputs

First Output

The operation of this output depends on what inputs are connected
to this node. If an object stream is input to this node, the output
is also an object stream containing the same objects as the input
(but with the data from this node attached).

If no object stream is
connected to this node, the output is a data output. This data
output can be connected to an Apply Data DOP,
or connected directly to a data input of another data node, to
attach the data from this node to an object or another piece of
data.

Locals

channelname

This DOP node defines a local variable for each channel and
parameter on the Data Options page, with the same name as the
channel. So for example, the node may have channels for Position
(positionx, positiony, positionz) and a parameter for an object name
(objectname).

Then there will also be local variables with the names
positionx, positiony, positionz, and objectname. These variables
will evaluate to the previous value for that parameter.

This previous value is always stored as part of the data attached to the
object being processed. This is essentially a shortcut for a
dopfield expression like:

dopfield($DOPNET, $OBJID, dataName, "Options", 0, channelname)

If the data does not already exist, then a value of zero or an
empty string will be returned.

DATACT

This value is the simulation time (see variable ST) at which the
current data was created. This value may not be the same as the
current simulation time if this node is modifying existing data,
rather than creating new data.

DATACF

This value is the simulation frame (see variable SF) at which the
current data was created. This value may not be the same as the
current simulation frame if this node is modifying existing data,
rather than creating new data.

RELNAME

This value will be set only when data is being attached to a relationship
(such as when Constraint Anchor DOP is connected to the second, third, of
fourth inputs of a Constraint DOP).

In this case, this value is set to the
name of the relationship the data to which the data is being attached.

RELOBJIDS

This value will be set only when data is being attached to a relationship
(such as when Constraint Anchor DOP is connected to the second, third, of
fourth inputs of a Constraint DOP).

In this case, this value is set to a
string that is a space separated list of the object identifiers for all
the Affected Objects of the relationship to which the data is being
attached.

RELOBJNAMES

This value will be set only when data is being attached to a relationship
(such as when Constraint Anchor DOP is connected to the second, third, of
fourth inputs of a Constraint DOP).

In this case, this value is set to a
string that is a space separated list of the names of all the Affected
Objects of the relationship to which the data is being attached.

RELAFFOBJIDS

This value will be set only when data is being attached to a relationship
(such as when Constraint Anchor DOP is connected to the second, third, of
fourth inputs of a Constraint DOP).

In this case, this value is set to a
string that is a space separated list of the object identifiers for all
the Affector Objects of the relationship to which the data is being
attached.

RELAFFOBJNAMES

This value will be set only when data is being attached to a relationship
(such as when Constraint Anchor DOP is connected to the second, third, of
fourth inputs of a Constraint DOP).

In this case, this value is set to a
string that is a space separated list of the names of all the Affector
Objects of the relationship to which the data is being attached.

ST

This value is the simulation time for which the node is being
evaluated.

This value may not be equal to the current Houdini time
represented by the variable T, depending on the settings of the DOP
NetworkOffset Time and Time Scale
parameters.

This value is guaranteed to have a value of zero at the
start of a simulation, so when testing for the first timestep of a
simulation, it is best to use a test like $ST == 0 rather than
$T == 0 or $FF == 1.

SF

This value is the simulation frame (or more accurately, the
simulation time step number) for which the node is being evaluated.

This value may not be equal to the current Houdini frame number
represented by the variable F, depending on the settings of the DOP
Network parameters. Instead, this value is equal to
the simulation time (ST) divided by the simulation timestep size
(TIMESTEP).

TIMESTEP

This value is the size of a simulation timestep. This value is
useful to scale values that are expressed in units per second, but
are applied on each timestep.

SFPS

This value is the inverse of the TIMESTEP value. It is the number
of timesteps per second of simulation time.

SNOBJ

This is the number of objects in the simulation. For nodes that
create objects such as the Empty Object node,
this value will increase for each object that is evaluated.

A good way to guarantee unique object names is to use an expression
like object_$SNOBJ.

NOBJ

This value is the number of objects that will be evaluated by the
current node during this timestep. This value will often be
different from SNOBJ, as many nodes do not process all the objects
in a simulation.

This value may return 0 if the node does not
process each object sequentially (such as the Group
DOP).

OBJ

This value is the index of the specific object being processed by
the node. This value will always run from zero to NOBJ-1 in a given
timestep. This value does not identify the current object within the
simulation like OBJID or OBJNAME, just the object’s position in the
current order of processing.

This value is useful for generating a
random number for each object, or simply splitting the objects into
two or more groups to be processed in different ways. This value
will be -1 if the node does not process objects sequentially (such
as the Group DOP).

OBJID

This is the unique object identifier for the object being
processed. Every object is assigned an integer value that is unique
among all objects in the simulation for all time. Even if an object
is deleted, its identifier is never reused.

The object identifier
can always be used to uniquely identify a given object. This makes
this variable very useful in situations where each object needs to
be treated differently. It can be used to produce a unique random
number for each object, for example.

This value is also the best way
to look up information on an object using the dopfield expression
function. This value will be -1 if the node does not process objects
sequentially (such as the Group DOP).

ALLOBJIDS

This string contains a space separated list of the unique object
identifiers for every object being processed by the current node.

ALLOBJNAMES

This string contains a space separated list of the names of every
object being processed by the current node.

OBJCT

This value is the simulation time (see variable ST) at which the
current object was created.

Therefore, to check if an object was created
on the current timestep, the expression $ST == $OBJCT should
always be used. This value will be zero if the node does not process
objects sequentially (such as the Group DOP).

OBJCF

This value is the simulation frame (see variable SF) at which the
current object was created.

This value is equivalent to using the
dopsttoframe expression on the OBJCT variable. This value will be
zero if the node does not process objects sequentially (such as the
Group DOP).

OBJNAME

This is a string value containing the name of the object being
processed.

Object names are not guaranteed to be unique within a
simulation. However, if you name your objects carefully so that they
are unique, the object name can be a much easier way to identify an
object than the unique object identifier, OBJID.

The object name can
also be used to treat a number of similar objects (with the same
name) as a virtual group. If there are 20 objects named "myobject",
specifying strcmp($OBJNAME, "myobject") == 0 in the activation field
of a DOP will cause that DOP to operate only on those 20 objects. This
value will be the empty string if the node does not process objects
sequentially (such as the Group DOP).

DOPNET

This is a string value containing the full path of the current DOP
Network. This value is most useful in DOP subnet digital assets
where you want to know the path to the DOP Network that contains the
node.

Note

Most dynamics nodes have local variables with the same names as the
node’s parameters. For example, in a Position node,
you could write the expression: